1. Field of the Invention
The present invention relates to an indicator device in which output light from a light emitting element is let to strike on a light incidence surface formed on a side face of a light conducting plate, where it is conducted inside the light conducting plate, and is let to outgo through a light output surface formed narrow in width and elongate on another side face having a prescribed spaced position relative to the light incidence surface, thereby allowing for the light output surface to be clearly lighted for indication, with a secured evenness of luminance of light over the light output surface.
2. Description of the Related Art
Generally, the indicator device as well as the illumination device is configured with a light emitting element using an LED (light emitting diode), lamp, or such, and a light conducting plate using a transparent acrylic resin, polycarbonate resin, or such, making output light from the light emitting element strike on a light incidence surface of the light conducting plate, where it is conducted inside the light conducting plate, and is let to go outside from a light output surface, for applications to a lighted indication, illumination, etc.
As such type of indicator devices, there are those to be fixed to a front panel of an electronic device, for a lighted indication of an operated state of the electronic device (refer to the first patent document “Japanese Patent Application Laid-Open Publication No. 2007-184191”, for example).
Further, as such type of illumination devices, there are surface illumination devices to be used as a backlight for liquid crystal display panels (refer to the second patent document “Japanese Patent Application Laid-Open Publication No. 2000-149635”, for example).
FIG. 1 is a side view of an indicator device 110 as a first example in the past, FIG. 2A, a top view of a surface illumination device 120 as a second example in the past, and FIG. 2B, a longitudinal sectional view of the surface illumination device 120.
Brief description is now made of the indicator device 110 illustrated in FIG. 1, which is disclosed in the first patent document.
As shown in FIG. 1, the indicator device 110 is fixed to a front panel 111 of an electronic device, to provide a lighted indication of an operated state of the electronic device.
The indicator device 110 includes a wiring board 112 with an LED 113 mounted thereon, the LED 113 facing a light incidence surface 114a at an end of a light conducting lens 114, which is formed, using a flexible material such as a vinyl chloride resin, in a polygonal or circular shape in section and bent substantially in an L form. The light conducting lens 114 has a reflecting surface 114b formed at another end thereof having a spaced position at a prescribed distance D relative to the light incidence surface 114a, the other end being bent in the L form, and a light output surface 114c formed at a far end thereof that faces a display window 111a of the front panel 111.
A bridge member 115 interconnects the LED 113 and the light conducting lens 114 with each other, the light conducting lens 114 being supported near the far end by a planer solid member 116 welded to a boss 111b of the front panel 111.
The light conducting lens 114 made of a transparent flexible material is adapted for the light incidence surface 114a to be variable in position relative to the LED 113, allowing for a sufficiently high light intensity at the display window 111a of the front panel 111.
Brief description is now made of the surface illumination device 120 illustrated in FIGS. 2A and 2B, which is disclosed in the second patent document.
As shown in FIGS. 2A and 2B, the surface illumination device 120 is used as a backlight of a liquid crystal display panel 126.
The surface illumination device 120 includes an LED light source 122 disposed inside a holder 121, in a lower region thereof at the side of a side face 123a of a light conducting plate 123 made of a highly transparent material such as a polycarbonate resin or acrylic resin. The light conducting plate 123 is provided with a reflection sheet 124 attached to a downside 123b thereof, and a diffusion sheet 125 attached to an upside 123c thereof, the diffusion sheet 125 having the liquid crystal display panel 126 mounted thereon.
The light conducting plate 123 has, at the medial side of the side face 123a, a light diffusion hole 123d formed as a through hole or concave hole on an optical axis K of the LED light source 122, whereby rays of light output from the LED light source 122 are separated into rays of light totally reflected by a circumferential surface of the light diffusion hole 123d in the light conducting plate 123 and rays of light passing through a central region or near of the light diffusion hole 123d, so that rays of light taken into the light conducting plate 123 are transversely diffused to thereby provide a homogenized luminance distribution, allowing for the liquid crystal display panel 126 to be evenly illuminated with rays of light output from the diffusion sheet 125, including those having passed through the light conducting plate 123 and those having been reflected by the diffusion sheet 125.
In the indicator device 110, output light from the LED 113 is let to strike on the light incidence surface 114a of the light conducting plate 114 bent substantially in an L form, where it is conduced inside the light conducting plate 114, via the light reflecting surface 114b, and is let to outgo through the light output surface 114c, whereby output light from the light output surface 114c can be displayed in the display window 114a of the front panel 111, as a lighted indication in a polygonal form or circular form in accordance with the shape in section of the light output surface 114c. However, there are some developed situations in which it is desirable, in the viewpoint of a design to the front panel 111, to form the light output surface 114c of the light conducting plate 114 with an arrow and elongate shape different from the above, and in such a case, for the light conducting plate 114 which is made of a flexible material, it would result in a discrepancy in strength to form a narrow and elongate surface for a lighted indication by using the flexible material.
There thus has been a desideratum for an indicator device having such a narrow and elongate surface for a lighted indication as shown in FIG. 3A, FIG. 3B, or FIG. 4 below.
FIG. 3A is a perspective view of a light output surface of an indicator device 130 as a third example in the past, FIG. 3B, a perspective view of the indicator device 130, FIG. 4, a perspective view of an indicator device 140 as a fourth example in the past, and FIG. 5, a graph showing an output light intensity characteristic of a typical LED.
As shown in FIG. 3A and FIG. 3B, the indicator device 130 is configured with an LED 131, and a light conducting plate 132 made in a planer form by using a transparent acrylic resin or the like, such that output light from the LED 131 is let to strike on a light incidence surface 132a made in a semi-circular form on a side face of the light conducting plate 132, where it is conducted inside the light conducting plate 132, and is let to outgo through a light output surface 132b made narrow in width and elongate on another side face having a spaced position at a prescribed distance D relative to the light incidence surface 132a, to thereby implement a favorable lighted indication in the viewpoint of a design in application of the light output surface 132b of the light conducting plate 132 to a front panel of an electronic device (not shown).
However, for the indicator device 130, as generally shown in FIG. 5, output light of LED 131 has substantially an elliptically-deformed circular characteristic in light intensity, whereby output light from the LED 131 is substantially elliptically spread in the light conducting plate 132, as illustrated by broken lines about an optical axis K of the LED 131 as a center, so that the light output surface 132b, which is made narrow in width and elongate in the light conducting plate 132 made in a planer form, would be lighted for indication to be light within a vicinity of a longitudinal center thereof, and would be lighted for indication to be dark in vicinities of both longitudinal ends of the light output surface 132b. 
It is noted that FIG. 3A illustrates a light outputting state of the light output surface 132b formed on the light conducting plate 132 that is separated into light and dark regions defined with a boundary line in between for descriptive purposes, while typically the brightness is gradually changed.
On the other hand, as shown in FIG. 4, the indicator device 140 is configured with an LED 141, and a light conducting plate 142 made substantially in an L-bent form by using a transparent acrylic resin or the like, such that output light from the LED 141 is let to strike on a light incidence surface 142a made in a semi-circular form on a side face of the light conducting plate 142, where it is conducted inside the light conducting plate 142 and reflected by a reflecting surface 142b made on another side face having a spaced position at a prescribed distance D relative to the light incidence surface 142a, and thereafter, is let to outgo through a light output surface 142c made narrow in width and elongate on the end face of a portion of the L-bent form at the end of the other side face, to thereby implement a favorable lighted indication in the viewpoint of a design in application of the light output surface 142c of the light conducting plate 142 to a front panel of an electronic device (not shown).
However, also for the indicator device 140, like the above, output light of LED 141 has substantially an elliptically-deformed circular characteristic in light intensity, whereby output light from the LED 141 is substantially elliptically spread in the light conducting plate 142, as illustrated by broken lines about an optical axis K of the LED 141 as a center, so that the light output surface 142c, which is made narrow in width and elongate in the light conducting plate 142 made substantially in an L-bent form, would be lighted for indication to be light within a vicinity of a longitudinal center thereof, and would be lighted for indication to be dark in vicinities of both longitudinal ends of the light output surface 142c. 
It is noted that FIG. 4 illustrates a light outputting state of the light output surface 142c formed on the light conducting plate 142 that is separated into light and dark regions defined with a boundary line in between for descriptive purposes, while typically the brightness is gradually changed.
As a solution to problems that would outcome in application of the indicator device 130 or the indicator device 140, there might be a method of applying a technical concept of the indicator device 120 having been described with reference to FIG. 2A and FIG. 2B, so that the light conducting plate 132 or 142 might have a light diffusion hole (not shown) formed therein as a through hole or concave hole on the optical axis K of the LED 131 or 141, respectively. However, for rays of light output from the LED 131 or 141, it is quite unclear, among others, how much they might be reflected and how much they might be blocked by the light diffusion hole, there being involved uncertainties for the light output surface 132b or 142c, which is made narrow in width and elongate in the light conducting plate 132 or 142, respectively, to be evenly lighted for indication in vicinities of both longitudinal ends thereof with substantially the same brightness as in a vicinity of the longitudinal center, constituting a difficulty to provide the indicator device 130 or 140 with a favorable quality of lighted indication.